The present invention pertains to the radio communication art and, more particularly, to a radio transmitter frequency multiplier.
The communication art, particularly in the field of radio frequency transmission, has developed numerous means for frequency multiplication. The need for frequency multiplication arises, for example, in radio transmitters wherein a high radio frequency carrier must be generated. Here, it is common to generate a submultiple of the desired signal in a conventional oscillator and follow the oscillator with a multiplier chain which outputs the desired multiple frequency.
One common multiplier design utilizes parametric frequency multiplication. Generally, a bipolar transistor is biased as an active stage with the oscillator signal applied at either its emitter or base. Non-linearities in the transistor due to the exponential voltage/current relationship of its emitter base junction as well as the non-linear base collector depletion capacitance versus applied voltage cause harmonics of the input signal to appear in the collector. Subsequent filtering is used to select the desired harmonic signal.
Such prior art parametric amplifiers suffer two defects. Firstly, they are inefficient. The generation of sufficient amplitude harmonic signals requires that a very large oscillator signal be applied at the stage's input. In addition, such parametric amplifiers are generally not adaptable for wide bandwith operation. This results from the fact that the load generally presented to the collector of the bipolar stage exhibits a widely varying reactive component as a function of frequency.